1. Field of the Invention
This invention relates to water activated batteries, a known category of batteries designed to remain inactive when kept dry and to begin generating an electric current rapidly upon activation by contact with an aqeuous solvent such as sea water or fresh water.
Such batteries find use on life rafts, life vests, survival kits and the like to power a signal light for use in an emergency and other types of electrical equipment.
2. Prior Art.
Khasin U.S. Pat. No. 5,424,147 discloses a water activated battery in which the cathode comprises a skeletal frame including conductive metal and having a portion of its surface area formed as open spaces, and further comprising a heat pressed rigid static bed of active cathode material encompassing the frame and formed of cuprous chloride, sulfur, carbon and a water ionizable salt. The only water ionizable salts disclosed are sodium chloride and calcium sulfate, and a preference is expressed for salts that are sparingly soluble in water having a solubility of less than 50 grams per liter (see col 3 lines 15-16).
Rao U.S. Pat. No. 5,225,291 disclosed a water actuated battery including a plurality of electrochemical cells including a "hybrid cathode member" which is described (col 3 lines 21-28) as formed of a material exhibiting inertness (low corrosion) such as nickel, stainless steel, titanium, graphite, carbon etc suitably subjected to catalytic activation. There is no mention of a cuprous halide ingredient.
Japan 53-4824 (Yuasa 1978) discloses a sea water battery of specified design in which the cathode contains silver chloride, copper chloride, copper sulphate or manganese dioxide. There is no mention (in the English language abstract) of graphite as a constituent of the cathode.
Japan 47-43887 (Yuasa 1972) discloses a magnesium salt-water cell including a silver chloride, copper chloride, manganese dioxide, air etc cathode and further containing a crystalline or glassy water-soluble weak acid or its anhydride. The only specific "weak acid or anhydride" disclosed (in the English abstract) is tartaric acid.
Chubb U.S. Pat. No. 2,658,935 discloses a magnesium--cuprous chloride "meterological" or "one-shot" battery in which the cuprous chloride electrode is porous and contains a cuprous chloride paste containing finely ground cuprous chloride,water, and a solution of a high polymer such as polystyrene in an organic solvent, optionally a plasticizer for the polystyrene, and various inert conductive materials added to improve the conductivity of the cuprous chloride such as carbon black or graphite.
Resnick et al U.S. Pat. No. 4,085,071 discloses fluorinated ion exchange polymers formed by hydrolysis of a precursor polymer containing pendant side chains with sulfonyl fluoride groups, and use thereof in the electrolysis of an aqueous solution of an alkali or alkaline earth metal halide to produce hydrogen and the corresponding halogen and metal hydroxide, as in the chlor-alkali industry. Here the ion exchange polymer replaces separators in the electrolytic cell which must withstand a hostile environment such as highly alkaline pH as well as exposure to chlorine and concentrated brine at temperatures approaching 100.degree. C. There is no suggestion of the applicability of such polymer to service in a water activated battery in which the conditions are entirely different.
There still remains a need for an improved water-activated battery able to activate rapidly in both salt and fresh water and to maintain its ability to power a signal light or other electrically powered device for extended periods.